a) Field of the Invention
The invention is directed to a detector arrangement for energy measurement of pulsed x-ray radiation, particularly for monitoring the energy emitted by pulsed EUV radiation sources.
b) Description of the Related Art
In the lithography process for semiconductor fabrication, the dose radiated into the photosensitive resist is a critical quantity. Therefore, during exposure the exact output of the radiation source must be known and must be kept constant. Photodiodes are typically used for output measurement, but they age due to the impinging radiation and their sensitivity changes. As a result, when such detectors are used for energy regulation, the EUV radiation sources show a long-term drift of the output power of the light source. In order to prevent this, regular reference measurements and recalibration are necessary or the detector must be exchanged.
The cause of this disadvantageous phenomenon in conventional semiconductor detectors is essentially that these detectors themselves absorb high-energy radiation (shortwave VUV or EUV radiation). This brings about electronic changes in the light-sensitive detector material resulting in changes in the sensitivity and response function of the detector, i.e., the detector is degraded. A radiation receiver of this type which is not stable over the long term and which does not allow absolute measurements can only be used for monitoring the radiation dose and for controlling the pulse energy of VUV radiation sources and EUV radiation sources if it is frequently recalibrated or exchanged. This process is time-consuming and reduces the long-term drift only by small amounts in short time periods.